Conventionally, as electrical mechanical conversion elements such as a drive element and a sensor, piezoelectrics such as PZT (lead zirconate titanate) are used. In recent years, in order to meet requirements for reducing the size of devices, densely packing the devices and reducing the cost of the devices, MEMS (micro electro mechanical system) elements using Si substrates have been increasing. In order to apply a piezoelectric to a MEMS element, it is preferable to reduce the thickness of its film.
By reducing the thickness of the film, it is possible to perform highly accurate processing using a semiconductor process technology such as film formation and photolithography, with the result that it is possible to realize size reduction and dense packing. Moreover, since it is possible to perform simultaneous processing on a large-area wafer, it is possible to reduce the cost. Furthermore, the efficiency of conversion of the mechanical into the electrical is enhanced, and the property of a drive element, the sensitivity of a sensor and the like are advantageously enhanced.
As a method of forming a film of a piezoelectric such as PZT on a substrate of Si (silicon) or the like, chemical methods such as a CVD method, physical methods such as a sputtering method and an ion plating method and liquid-phase growth methods such as a sol-gel method are known. PZT formed into the film performs a satisfactory piezoelectric effect when its crystal has a perovskite structure.
A PZT film formed on the electrode of the Si substrate is a polycrystal where a plurality of crystals gather in the shape of a column because the lattice constants of the crystals of the electrode differ from each other. It is known that, in the columnar crystals described above, the more crystals grow in the film thickness direction on the same crystal plane (the more the orientation is increased), the more the piezoelectric property of the film is enhanced.
In recent years, it has been required to further enhance the property of a piezoelectric film such as PZT. One way to enhance the piezoelectric property as described above is to enhance a relative permittivity and the piezoelectric property by adding an impurity. It is known that in particular, in a piezoelectric having a perovskite structure (which ideally has a cubic unit lattice, which is a crystal structure formed with a metal A arranged in each vertex of the cubical crystal, a metal B arranged in a body center and an oxygen atom O arranged in each face center of the cubical crystal and which includes a tetragonal crystal, an orthorhombic crystal and a rhombohedral crystal where the cubical crystal is distorted), a substance called PLZT obtained by substituting La (lanthanum) which is an element that is one valence larger than Pb arranged in an A site has a high relative permittivity and a high piezoelectric constant.
For example, non-patent document 1 discloses that, in PLZT of a bulk ceramic, it is possible to obtain a high piezoelectric property with a predetermined amount of La added (for example, 8%).
However, when a thin film of PLZT is obtained by film formation, since crystallization is poor as compared with PZT, in the thin film, a high property obtained in bulk is not obtained
Hence, patent document 1 discloses a technology for forming a PLT layer free from Zr on a substrate and forming a PLZT layer on the PLT layer. In this technology, the PLT layer having satisfactory crystallization is used as an undercoated layer, and thus it is possible to enhance the crystallization of PLZT.